Saturday, October 31, 2015
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A reader has informed us (in the obsolete Blogger built-in comments: have you turned your Javascript off?) that Leo Philip Kadanoff died in Chicago on Monday, October 26th, 2015, from respiratory failure. He was 78 years old:

Kadanoff has done lots of fundamental work in statistical, nonlinear (chaos theory-related), and solid state physics. Look at the impressive citation counts. Except for the Nobel prize, he has won all the classical top medals in physics, including the National Medal of Science from Bill Clinton in 1999. He has also worked as the president of the American Physical Society.

During the funeral, his daughter modestly pointed out that when he was in his 50s, his switched from making discoveries to making great new people.

Friday, October 30, 2015
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Homi Jehangir Bhabha was born on October 30th, 1909, to a super-elite Indian family. The family was Parsi – the word clearly indicates some relationship to Persia and the words and indeed related. However, the Parsis are just one of the old nations that lived on the Persian territory a long time ago. These days, no Parsis live in Iran and there are only 60,000 Parsis in India and 15,000 Parsis in Pakistan. Quite a special group, relatively to 1+ billion of other Indians.

His father was a top lawyer but more importantly, the relatives included Sir Dinshaw Maneckji Petit, the top Indian textile mogul, and Dorabji Tata, the most famous Indian steel industrialist.

Thursday, October 29, 2015
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It was supposed to be a confrontation between the GOP candidates themselves and a comparison of their policies. Instead, it unavoidably morphed into a battle between politicians who care about the essence on one side; and demagogic superficial hostile journalists on the other side.

Ted Cruz has summarized the juvenile behavior of the would-be moderators most eloquently:

The questions basically were: Trump, are you a comic book villain? Carson, can you do math? Rubio, why won't you resign? Bush, why have your numbers fallen? The "moderators" were competing in pissing on the politicians. The comparison of the hosts' behavior in the Republican and Democratic debate reveals a huge asymmetry.

Wednesday, October 28, 2015
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Just a week ago or so, Bill Zajc sent me a mail announcing that he liked some texts by Matt Ridley, a British conservative journalist and a member of the House of Lords, who may be classified as a climate lukewarmer of a sort. You know, this "purple" political flavor is something that I share with him to the extent that I don't subscribe to every point believed by some conservative mass movements such as the U.S. evangelicals.

Well, I wouldn't count myself as a lukewarmer – I sympathize with Dick Lindzen's view that it's much more accurate for us to proudly call ourselves the deniers (because we don't have any significant doubt that the climate fearmongering is nonsensical) – but due to Ridley's pragmatic common sense attitude to many issues, you could think that I find his ideas close to my heart, too. But sometimes, there comes a shock. Most recently, Ridley wrote a rant titled

in the Wall Street Journal five days ago. He argued that basic science – or the funding for any science – isn't needed because the technological innovation is the only thing that matters and it occurs mostly automatically. It's done by regular people, sometimes workers, who are driven by purely practical motives. And Edison, Newton, Darwin, and all famous people of science and technology had lots of competitors who would do exactly the same anyway, so the big conclusion by Ridley is that discoverers don't actually find their discoveries. Instead, the discoveries are just automatically finding their discoverers and the character of the progress is becoming even more automatic in this sense as the computer epoch is advancing.

That's a great story that is right – except for the cases when this story is completely wrong, of course, and these "exceptions" actually represent the overwhelming (and increasingly overwhelming) majority of the progress of the mankind.

Composite photons supported by factorization in the presence of Wilson lines through wormholes

Let me begin with a general sociological observation.

A week ago, the world's most notorious anti-physics hate blog was talking about "fads" in fundamental physics. There are periods of focused excitement in which a large portion of the research community spends a lot of time with a certain topic and writes followup papers to a certain publication that has created a sufficient excitement.

In this case, the topic was "entanglement in quantum gravity", a concept that most quantum gravity experts found irresistible in recent 6 years or so. Previously, people would witness "fads" rooted in the construction of huge classes of realistic vacua (KKLT-like landscape), old matrix models, \(pp\)-waves, Matrix theory, Hořava-Lifshitz gravity, or entropic gravity (I mentioned the latter two to make it clear that in some cases, I consider the topics of the "fads" not too exciting or downright wrong, respectively), not to mention dozens of other topics.

Needless to say, the anti-physics blog was negative about the "fads" in general. I must say: "fads" are completely natural, allocate the intellectual potential reasonably, and make the researchers happy.

Tuesday, October 27, 2015
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A participant at a popular talk about light that I gave one month ago has found a difficult comment somewhere in my slides that has scared her and she used it as an example to argue that my talk was too hard. (Perhaps a good reason not to send such documents to random people.) It was something like:

For most photons emitted around us, the probability that light is emitted by the transition from the atomic level \(\ket {E_1}\) to the level \(\ket{E_0}\) is proportional to the squared matrix element of the electric dipole \(\vec{d}_{1,0} = \bra {E_1} \vec p \ket {E_0}\).

I didn't really discuss this issue verbally – because I did make an estimate that the expectation number of the number of people who would get totally lost was above 99.5% so most likely, no one would benefit – but I do believe that a scientifically educated yet cultural human beings should be aware of the claim above.

It really describes the "bulk" of the reason why there is light around us and how matter emits it.

Monday, October 26, 2015
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I received a copy of this beautiful book by Shing-Tung Yau and Steve Nadis that has increased my excitement about the possible future 100-kilometer \(100\TeV\) Great Collider of China.

Be ready for a 200-page book whose pages' area is greater than most books. Lots of the pages show photographs of physicists, experimental devices and facilities, and similar things. The book has its own domain, TheGreatCollider.com (comment added on Tuesday).

The name "Great Collider" has been coined by David Gross, along with the analogies with the Chinese representative among the Wonders of the World. His ancestors helped to build the Wailing Wall which is smaller but similar. And the relationship between the Great Wall and the Great Collider is not just an analogy. The Great Collider should be built near the Eastern end of the Great Wall of China. Its length, 100 kilometers, would still be modest in comparison with the 21,000 kilometer of the wall (this is the total length of all segments where any traces of a wall have been found by 2012; other numbers may be shorter) but it would still be by far the largest machine built by the humans.

Sunday, October 25, 2015
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Update: the answer turned out to be a resounding Yes. Law and Justice got 235/460, more than 1/2, of the deputies.

Today, Polish voters – descendant of Forefather Lech who was the brother of Forefather Czech – are choosing their new Parliament.

My God, a girl fight.

And it's sort of fun and unusual because both prospective prime ministers are female. But as some Polish "insider pundits" say, the women are just facades or puppets who fight on behalf of their male puppet masters.

Saturday, October 24, 2015
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This blog post is partially an advertisement of the blog written by a postdoc at the Perimeter Institute who studies fancy methods to calculate scattering amplitudes in gauge theory (very serious theoretical stuff!),

Thursday, October 22, 2015
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Let me try to explain in a maybe more physicists-friendly way essentially the same things that dalpezzo already mentioned beneath the "blog post about 1729". It is an exercise for experts to notice the hidden assumptions and oversimplified explanations.

Let \(X\) be a compact manifold. Let us consider \(U(1)\) gauge theory on \(X\), i.e usual Maxwell's electromagnetism. Locally on \(X\), the gauge field is a 1-form \(A\) and the field strength \(F=dA\) is a 2-form. If \(X\) has non-trivial 2-cycles, one can have non-trivial fluxes of \(F\) through these 2-cycles. The number of topologically inequivalent 2-cycles in \(X\) is \(B_2\), the second Betti number of \(X\) and, as the fluxes are quantized, a flux configuration is given by a collection \((n_1,\dots, n_{B_2})\) of \(B_2\) integers. It is easy to show that for any flux configuration, there exists a gauge field with the prescribed fluxes.

Quantum mechanics was first discovered by Heisenberg in 1925. As we can see with the hindsight today, it was the first time when even the basic logic of a physical theory was so intellectually demanding that even most of the people otherwise considered intelligent just weren't smart enough to "get it".

Albert Einstein, after he made all the important contributions of his career, became a celebrity on top of a brand new movement – a movement constantly producing totally wrong "objections" against quantum mechanics. While between 1935 and his death in 1955, Einstein was rightfully considered a hasbeen who had simply lost the contact with the state-of-the-art research in fundamental physics, the influence of the anti-quantum movement actually grew since the 1960s.

A vast majority of popular books on the subject of quantum mechanics literally live in an alternate reality. They try to present quantum mechanics as a suspect sitting on the bench – while some alternative theory proposed by Einstein or Bell or Bohm or Everett or Ghirardi or... plays the role of the judge. The only problem is that there exists no viable alternative theory. Quantum mechanics has been the only framework for a successful description of new experiments for more than 90 years and nothing at all has changed about the basics since that time.

Wednesday, October 21, 2015
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If you look at my long list of bumps and excesses that are waiting to be confirmed or (more likely) deflated by the continuing LHC experiments, you will notice one category of tantalizing hints that is larger than others: possible new Higgs bosons.

In 1988 or so, I had to attend rock'n'roll classes where I had to pretend to learn how to dance it and this piece released in 1986 was by far the most frequently played song over there. Not only because my talent for similar things is close to zero, it was so humiliating.

The Standard Model predicts one physical Higgs particle species, the boson whose mass has to be \(125\GeV\) to match the recent discoveries. But alternative theories with a richer field content predict new Higgs bosons. The minimal supersymmetric models predict that the God particle has five faces and there exist new sources of the Higgses, e.g. in the "next to minimal" theories.

Darkblue has promoted – and is still promoting – the thesis that only circular polarizations and not linear polarizations may exist for an individual photon. To strengthen his point, he also refers to a (zero-citation) preprint by two crackpots that proposed to experimentally "test" a similar nonsensical claim.

(Yes, these two authors – proud senior janitors at IEEE – and Darkblue clearly belong to the Šmoitian sect of morons who feel very self-confident whenever they say "we want to make an experiment", regardless of how stupid the experiment and especially its interpretation is.)

Among other gems, the paper claims that a linearly polarized photon moving in the \(z\)-direction should have \(J_z=0\hbar\). Well, the expectation value \(\langle J_z\rangle =0\hbar\) may be zero but the vanishing value is strictly forbidden as a result of a measurement (zero isn't among the eigenvalues): there are no longitudinal or scalar photons.

Monday, October 19, 2015
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Scott Aaronson is an extreme leftist – to the extent that he was once scheduled to get chemically castrated because he had concluded that a castrated complexity theorist is cleaner from the feminist viewpoint than an occasionally horny one – but you know, we are talking about the U.S. Academia where loons like Aaronson often end up being the moderates. And this topic is an example.

Aaronson talks about Ms Izabella Laba who is a mathematician but who has defended – e.g. in her tweets – the (far left) social and political scientists and their unnecessarily complicated jargon. Aaronson said "lashing Saudi women for driving cars" sounds more comprehensible than "exercising male privilege..." and the latter brings nothing new. Ms Laba claimed that the pompous would-be expert jargon has to be used for the same reason why "derivatives" appear when we talk about calculus.

Three months ago, I promoted (American-European and other) free trade in general and some characteristic Czech food product in particular. This blog post is dedicated to a similar light topic – in fact, to a retro hardcore version of it.

Xindl X (Mr Ondřej Ládek): "Czechacheque And Totacheque" (Little Czech Man And His Dear Totalitarian Regime) dedicated this song to the absurdity of some people's claim that life used to be better during communism

The German supermarket chain Lidl is doing very well in Czechia – I am pretty sure that much better than Tesco, Billa, and others. One of its bonus features are "weekly themes". Every week, the consumers may enjoy their American week or Mexican week or Spanish week or French week or Italian week or Greek week or British week or XXL week. Depending on the nationality, you may buy many of the typical products associated with one nation or another.

But the week that started today is arguably even more fancy. At least in Czechia, it's the Lidl Retroweek. See a PDF or interactive flier version of the weekly catalog. And it's so much fun that I even forgave our local Lidl for having given me no Stikeez today. (And the previous 3 Stikeez I got were identical, too bad!)

Saturday, October 17, 2015
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Anne Applebaum, a journalist, wrote an anti-Russian rant for the Slate and the Washington Post. The titles are Authoritarianism’s Fellow Travelers and Russia’s new kind of friends. The similarity of her texts to the anti-American and anti-dissent tirades I remember from the official communist press is hard to overlook.

Her main thesis – the thesis of this text just like the previous ones – is that whoever refuses to "hate" Russia and cooperate on the destruction of Russia or its current government or something of the sort has to be called out, demonized, and perhaps also isolated or punished. Czechia is the world's #1 source of the politicians she decided to defame. However, the reality is very different.

Russia is the largest country in the world (by area), an important business partner of many others (especially in Europe and especially because of the fossil fuels), and it's enjoying one of the most promising epochs in its history when it comes to the degree of freedom, prosperity, stability, and contributions to the peace in the world. It just happened that Russia also became the #1 country by effectiveness that started to do something against the Caliphate.

Not surprisingly, the approval rate of the Russian president and perhaps some other institutions is closer to 100% than to 50%. Everyone who is thinking about the "isolation" of this country or some kind of removal of its government is either a jihadist or a full-fledged sociopath or both. Nothing like that may "naturally" occur without some kind of a big war that no decent person in the world wants.

But Ken Ono (not to be confused with John Lennon) and his graduate student Sarah Trebat-Leder from Emory University, Georgia (not in the former Soviet Union but in the former Confederate States of America) have just published a playful mathematical paper with some close enough ties to string theory:

Thursday, October 15, 2015
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Prof Geoffrey Marcy, the world's most famous single discoverer of exoplanets, found himself in the hot sea of jihad-style hostility and resigned yesterday. Over the decades of his successful career, aside from having discovered many new worlds including the very first exoplanet exactly 20 years ago these days (with Butler), the first Neptune-size planet, and many others, this natural hugger may have given a short neck massage (in his car, through the clothes!) to his friend who was undergraduate. He may have touched the leg of a student, hugged a few other students, kissed one or two, and done five more comparable things to several other female scientists.

Only indirectly related: Worlds Apart at Russia Today, a 30-minute interview with Czech ex-president Klaus about the fall of communism, political correctness, decline of the West, fallacies of the European integration, Ukraine, dissolution of Czechoslovakia, migration, causes of the Middle East mess, America as Socialist Europe Lite, wrong U.S.-EU analogies etc. I must say that Oksana Boyko, the host, obviously knows a lot about Klaus' ideas and the history of our country and in some points of the interview, she may have even looked like a sharper thinker than Klaus (just one example: her usage of Milton Friedman's F-twist as an argument was high-tech); I say it even though I am almost certainly closer to his views. If he reads these lines, and he often is, I am sure that he will survive – I still liked it. ;-)

Whether he has done anything that would go beyond these absolutely innocent acts is being disputed and even the University of California "panel" that has investigated those things admitted that the probability is only around 50% that something "worse" (like the motion of his hand from the thigh closer to the belly) has ever happened. But this complete absence of the data that would imply that he has done something unequivocally annoying hasn't prevented a certain community from a hysterical reaction that has, from many viewpoints, exceeded the anti-Jewish campaigns in Germany of the 1930s.

In the new story about the harassment, we learn that in several incidents, Marcy has clearly violated some strict rules of the professional behavior. While it is obvious that his behavior wasn't kosher and he must have found himself in trouble, the most "damning" stories are still amusing.

Already ten years ago, he gave a ride to his new undergraduate friend. He shared his opinions on whether she should leave her boyfriend and started to give her neck message. She didn't protest. Now, she says that it wasn't because she liked it. Instead, it was because she needed a recommendation letter. It's obviously hard to prove that her feelings and reasoning were one way or another. It's not surprising that his behavior raises some eyebrows but I would still insist on the presumption of innocence.

Tuesday, October 13, 2015
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Angus Deaton became the 6th Princeton-affiliated scholar to have won the memorial Nobel prize in economics. He received one megadollar for his work on poverty and inequality. I wasn't too actively aware of this Gentleman and his work but he seems pretty interesting.

He has apparently done lots of the difficult microscopic work in collecting and interpreting the local household data in India and other poor countries. But he's had some disagreement with Bill Gates which finally made me interested in the question what Deaton actually thinks about poverty, aid programs, and other things.

by Großardt and 3 co-authors is to test the idea that much of the world obeys the principles of quantum mechanics but gravity is classical. Such a combination is referred to as the "semiclassical gravity" and it is often used as an approximation to describe various things. (It was the approximate framework in which Hawking derived the black hole radiation for the first time.) Because the gravity is classical in this would-be theory, so is the spacetime geometry. "Semiclassical gravity" effectively ends up being equivalent to quantum field theory in a classical background geometry.

Sunday, October 11, 2015
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As predicted, Mercedes, Honda, Mazda, Mitsubishi also have emissions an order of magnitude above "test" numbers

From the beginning of the Dieselgate around September 21st, I've been bothered by lots of things about the hysteria. It is clearly a great example of the insanities that become unavoidable when the society is overregulated, governed by bureaucrats detached from the real world and technology and inventing lots of arbitrary restrictions on the products. The people and corporations have to live so they obviously have to find their way through this jungle of counterproductive regulations.

But one of the issues that has touched me at the deeply ethical level was the way in which the Volkswagen Group was singled out. It has always seemed basically obvious to me that the emissions from diesel cars of different brands have to be basically the same. I wrote, among other things,

However, the emissions that have been manipulated also include the oxides of nitrogen. And those are harmful, I think. However, I don't really believe that different diesel cars differ so terribly much from each other when it comes to NOx emissions. All of the diesel motors burn the diesel fuel and it must chemically mean pretty much the same thing.

Needless to say, I was attacked by the brainwashed Volkswagen bashers and ecomentals.

Friday, October 09, 2015
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The following 10-minute video shows an exchange between the GOP presidential candidate Ted Cruz and Aaron Mair, the current president of the Sierra Club, who was a witness in the Congress.

Sierra Club is an environmental organization founded in 1892. The organization supports the climate alarmism in the maximum way. Normally, you would expect the president of an organization that says to care about the Earth and the environment – and the climate – to know at least something. You would normally expect he knows more than a conservative Republican politician.

who is getting her PhD under David Kutasov at the University of Chicago. She has written almost a dozen of papers and cooperated with folks like Klebanov etc. at Princeton and Ooguri etc. at Caltech, not to mention interactions with Jeff Harvey in Chicago and others.

Also, RAF III was able to notice that the thesis refers to a 2013 TRF blog post. I assure you, it's not usual to cite blog posts and the technical author needs some balls to do a thing like that in an otherwise formally flawless technical piece of work. Thanks for that, Jennifer!

Jennifer cites my blog post as the first source of the observation that the "existence or non-existence of a [non-traversable] wormhole in quantum gravity" is not observable by a well-defined apparatus or a procedure; and, correspondingly, it is not an observable in the theoretical sense (i.e. a linear Hermitian operator). This negative statement has to hold because the "existence of entanglement", which is dual to it, isn't an observable, either.

Thursday, October 08, 2015
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Days after the Nobel peace prize winner Barack Obama has flattened the Afghani hospital of a fellow Nobel peace prize winner, Doctors Without Borders, the prospective Nobel peace prize winner Angela Merkel has made some new insane statements meant to increase her chances to beat Tunisia's National Dialog Quartet (unlikely!) and win the 2015 Nobel peace prize for having caused the worst migration wave in Europe since the end of the Second World War.

Before I get to her explicit statements, I want to dedicate a few paragraphs to a meme that has been mentioned on this blog but as far as I remember, it was never a major topic of a blog entry. Some people say that the post-communist countries should support the immigration from the Muslim world because the citizens of these countries have been allowed to emigrate to the West during the Cold War years and these Eastern countries should therefore repay the debt.

This suggestion is insane. The countries have nothing to be grateful for. On the contrary. The emigration has stripped our homelands of some gold in the human capital.

Wednesday, October 07, 2015
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There are tons of ongoing events outside physics that are happening and that would normally be discussed in separate blog posts. Let me reduce the number of blog posts where these heavily unphysical topics appear and consolidate my comments.

Russians in Syria

My most recent entry about Syria was posted hours before the Russian lawmakers okayed an operation in Syria – which was followed by the ongoing airstrikes that started just several more hours later. The bombing videos remind me of what we were watching in the early 1990s when Bush 41 was showing Saddam that the occupation of Kuwait wasn't a good idea.

It's obvious that the Russian intervention is making a difference – and a much bigger difference than the year(s) of the U.S. alleged campaign. I think that the data make it extremely probable that the U.S. was just "pretending" to be fighting against the Islamic State. Russia has already destroyed a significant portion of the tanks, command centers etc. It is implausible that this won't make a difference on the ground rather soon. It's like playing chess so that one piece of your enemy is artificially eliminated after every move.

Tuesday, October 06, 2015
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The 2015 Nobel prize in physics went to Takaaki Kajita (University of Tokyo, 1/2) and Art McDonald (Queen's University, Ontario, Canada, 1/2), for their discovery of the neutrino oscillations – which may also be interpreted as the discovery of the neutrino mass. Congratulations!

I don't think that I know the Gentlemen in person. Of course, I know their achievements in cooking. A fajita is a flavored meat strip. And it's sensible that fajitas got the prize along with the hamburgers. McDonald's restaurants have repeatedly saved my life, for example in Santa Cruz, California. While I was at Harvard, I often walked a mile towards the Central Square, away from the hard core of the People's Republic of Cambridge which de facto bans corporations such as McDonald's. (This attitude of the pompous far left-wing bigots offends my nationalist feelings as well – McDonald's only became a big chain when it was bought by Ray Kroc, 1902-1984, a Czech American whose father was born 10 miles from my home.)

But back to the prize. It's a prize in particle physics and one that is totally legitimate but I am sure that lots of top particle physicists will be left a bit unexcited by that prize, too. For example, Nima Arkani-Hamed – who, as a Westerner, is primarily Canadian, just like McDonald – has explicitly stated that neutrino physics – something that the Fermilab has pretty much promoted to the core of the institute's activities – isn't an adequate flagship for the particle physics enterprises in a country that is as great as the U.S. I have always shared this view.

Monday, October 05, 2015
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Ann has sent me Frank Wilczek's new popular book, "A Beautiful Question" (thank you again, Ann!) and it is very nice, entertaining, multi-dimensional, and mostly correct. The question reads "Is the Universe built upon beautiful ideas?" and Wilczek's highly secret answer is a combination of the letters Y, E, S.

If you don't know the name, Frank Wilczek is a Twitter follower of mine. (You probably despise honors but he is also a 2004 Nobel prize winner.)

The book describes the history and recent developments in "generalized physics" and is nicely built around the condensation nucleus called "beauty". It's possible but sometimes, one can see that the presentation of the topics is a bit stretched. Is the history of physics a history of beauty? The answer is as ambiguous as in the case of history of physics as the history of light. Yes, no, a little bit, perhaps. Well, the beauty is great if you see it in the laws of Nature. But if you don't see it, it's likely that it's your fault, not Nature's. A person's sense of beauty is only a good guide to understand Nature if the person has a good sense of beauty, one that is correlated with Nature's. ;-)

Saturday, October 03, 2015
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I have also mentioned another text in the same issue of the e-magazine, Life Is a Braid In Spacetime, by Mad Max Tegmark, but I think that it's even more vacuous than his well-known texts about the Mathematical Universe. His text is equivalent to: There is a spacetime. Something is mathematical about it. Sometimes it's the future, sometimes it's the past. If one is a bird, he can look from a bird's perspective. If he is a frog, he may have a frog's perspective.

If it won't be raining, we won't get soaked. (The previous sentence is from a popular Czech children's song that was the template for Smetana's The Moldau ;-) and that I began to use as a symbol of tautologies and "easy prophesies".)

Life is complicated. World lines of living things are complex, too. Yup but where's the beef, Max? Thed text is like Gigi's Puzzle in the Fio Bank's TV commercial: Which of us is me: he... or me...? – He [while each solver points at a different man]. – The solver #1 is a moron moron, the solver #2 is an imbecile moron.

Thursday, October 01, 2015
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Most of it is an attempt to explain the important idea that most theories we use in physics are effective theories that are optimized for certain scales – for phenomena whose typical energy or typical length belongs to a certain fuzzily defined interval. It would be great if someone were explaining this important point, an unsung scientific revolution, as Krauss correctly calls it.

But he stops short of doing it right – and goes well beyond that, too. The insights about the renormalization groups aren't the goal of his tirade. Instead, they are just some new tools in Krauss' lame attacks against state-of-the-art theoretical physics.

HTTPS: a technical detail: Blogger.com allowed me to activate https://motls.blogspot.com/ and I did so. The HTTPS URLs are no longer redirected; they are safe. Some widgets may be missing in HTTPS but I guess no one will miss those. ;-) HTTP works as it did before.

Petrol engines and diesel engines are comparably important. In the U.S., diesel isn't too popular but in Europe, the percentage of diesel engines in newly sold vehicles has actually surpassed 50%. The fuel economy of the diesel engines has traditionally been better (you may see lots of 2-liter diesel cars that run on less then 4.5 liters per km); but the diesel cars end up being a bit more expensive. Petrol and diesel engines have comparable bodies of supporters, however.

Environmentally, the two groups of engines are roughly similar but the details are very different. Diesel engines produce – and the producers have to care about – particulate and NOx emissions. NOx is harmful to the human health, especially lungs. As far as I can say, the most important measurements are the measurements of the NOx concentration at the most contaminated places of our cities. We know that the NOx concentrations have dropped considerably in recent decades.